This invention relates to the production of higher hydrocarbons from the lower alkanes. It is particularly applicable to the production of gasoline boiling range hydrocarbons from methane.
The need to supplement petroleum supplies has stimulated research and the production of chemicals and fuels from other sources. Methane from natural gas and from the conversion of coal is a source of considerable interest for such production.
It is well known that methane can be converted to methanol by reformation with steam and the methanol thus produced further processed over a crystalline aluminosilicate catalyst to form gasoline boiling range hydrocarbons. Such a process is described in U.S. Pat. No. 3,928,483 to Chang et al.
It is also recognized in PCT International Publication No. WO85/02608 that higher hydrocarbons can be prepared from substituted alkanes, particularly monohalomethanes, by reaction over crystalline aluminosilicate zeolite catalysts. Unfortunately, a continued problem with these processes is the destruction of the zeolite catalysts where water or HCl are present. It was believed that HCl de-aluminates crystalline aluminosilicates leading to their framework collapse and lost catalytic activity.
Monohalomethanes can be prepared as disclosed in European Patent Application No. 0117731 and as suggested in the above cited PCT Publication, converted to higher hydrocarbons over crystalline aluminosilicates. It has long been thought that the monohalides are much preferred in such processes with only low levels of polyhalogenated alkanes tolerated for effective conversion. Such monohalomethanes can be produced by reaction of chlorine or other halogens with methane which requires elevated temperatures above 450.degree. C. or by the oxyhalogenation of methane using a suitable catalyst such as the halide salts of copper, nickel, iron or palladium. Such procedures as are described in the above cited European Patent Application are characterized by low conversions, generally less than about 35%.
An oxyhydrochlorination catalyst containing copper chloride, potassium chloride and a rare earth chloride is disclosed in U.S. Pat. No. 4,123,389 to Pieters et al. This catalyst is reported to provide substantially higher values of methane conversion, but to result in substantial polychlorination. Previously this catalyst was of particular interest in the production of carbon tetrachloride as a feedstock for polychloro-refrigerants.
U.S. Pat. No. 4,513,092 to Chu et al. describes an attempt to combine catalysts for the halogenation-condensation of alkanes. In this patent, a dual-function catalyst including cupric halide, an alkaline earth halide or alkali metal halide and a rare earth halide on a crystalline aluminosilicate catalyst is disclosed. The catalyst is used to promote the conversion of methane to higher hydrocarbons in a single reactor. It is noted that methane conversions of less than 10 mole percent are reported. It is also noted in this reference that deleterious effects may result unless halogen acid gas concentrations are limited especially where such gases could combine with water.